On the PHPClasses.org site they've posted the latest episode of their "Lately in PHP" podcast series - Episode #30, "Will PHP6 Feature a JIT compiler?"

Now that Facebook made some progress with their PHP HipHop VM JIT compiler engine, some PHP core developers are considering having also a JIT compiler implementation of the official implementation based on LLVM, eventually in PHP 6. [...] They also commented on the first alpha release of PHP 5.5.0, proposals for having pure interfaces in the PHP core, the Facebook PHP JIT compiler enhancements, and the new system of levels and missions of the PHPClasses and JSClasses sites.